Manufacturing method for small electric lamps

ABSTRACT

The present disclosure provides a new method for manufacturing small electric lamps to be used within electronic machines, etc., particularly small electric lamps with long life and high quality, using a simplified process and equipment, e.g., by vacuum-sealing the entire filament-attached bead mount in a bulb, and then, with the bead mount set in position, heating from outside of the bulb to fuse together the bead of the bead mount and the bulb; small electric lamps thus produced; and the manufacturing equipment.

[4 1 Oct. 17,1972

United States Patent Hamai [541 MANUFACTURING METHOD FOR 7/1954 Hager..........................316/19 9/1966 Meier 1 6/19 3,275,879 9/1966 Demarest et a1.............316/19 SMALL ELECTRIC LAMPS [72] Inventor:

Jituo Hamai, Tokyo, Japan Primary Examiner-John F. Campbell Assistant ExamineF-Richard Bernard Lazarus Attorney-James E. Armstrong and Harold C. Wegner [22] Filed:

[57] ABSTRACT The present disclosure provides a new method for 211 App]. No.: 133,874

[30] Foreign Application Priority Data manufacturing small electric lamps to be used within June 19,1970 japanmmmu g 539 electronic machines, etc., particularly small electric June 19, 1970 Japan................ .....45/53917 lamps with long life and g quality, using a plified process and equipment, e.g., by vacuum-sealing the entire filament-attached bead mount in a bulb, and

,H01j 9/18 then, with the bead mount set in position, heating .316/17,18,19, 23, 24,1;

Int.

from outside of the bulb to fuse together the bead of [58] Field of Search..........

the bead mount and the bulb; small electric lamps thus produced; and the manufacturing equipment.

5 Claims, 10 Drawing Figures [56] References Cited UNITED STATES PATENTS 2,489,261 11/1949 Braunsdorff.................316/19 PATEN'TEDIJBI-l 1 1912 SHEET 3 BF 3 F/GJO MANUFACTURING METHOD FOR SMAL ELECTRIC LAMPS BACKGROUND OF THE INVENTION In the manufacture of small electric lamps it is important to assure perfect fusion between the bead of the bead mount and the bulb and to prevent infiltration of impure gas into the bulb being fused. Moreover, for mass production of such small electric lamps it is necessary that the manufacturing process and operation be simple; the production be finished in as short a time as possible; and the products be uniform in quality.

The conventional manufacturing of small electric lamps has the following drawbacks. in one method the heating element, the bulb and the bead mount are all placed in an airtight box; after evacuating the airtight box, theheating element is heated to fuse together the bulb and the bead of the bead mount. According to this method, when the heating element functions, impure gas generated from the bead and the heating element itself infiltrates into the bulb and gets sealed in the bulb, which is fused to the'bead. As the result the degree of vacuumin the bulb drops and in consequence the small electric lamp thus produced cannot give the required illumination, and its service life is shortened.

In another method, the bulb with its open end exposed and the bead mount with the bead exposed are held in a jig of high heat capacity and this jig is placed in a vacuum heating furnace. .Then resistance wire around this furnace is heated to heat and fuse together the open end of the bulb and the bead of the bead mount. Next, heating is stopped and the jig is pulled out of the furnace by means of a metal wire attached to the jig. In this method, too, impure gas generated from the metal jig holding the bead mount and the bulb, the jig support and the metal wire attached to this support, when they are heated, infiltrates into the bulb which is fused to the bead and the bead mount, and 'in'c'onsequence inevitably the same problems occur as in the first method.

In still another method, the inside of the bulb,'which holds the entire bead mount, is evacuated through the open end of the bulb by means of an exhaust pipe, etc.; then from outside of the bulb, the bulb and the bead of the bead mount are heated and fused together by a gas burner, etc. v 1

According to this method, the inside of the bulb is under vacuum and the outside of the bulb is under atmospheric pressure, with a wide difference in pressure between inside and outside of the bulb. Thus, when the burner is applied on the outside of the bulb, the bulb glass melts and softens, coming into contact with the bead of the bead mount, before the bead of the bead mount can become soft enough to fuse with the bulb. This contact seems to result in fusion and sealing of the head of the bead mount and the bulb, but actually the bead of the bead mount is often sealed while insufficiently softened. The lamps with thus imperfectly fused and sealed beads are liable to be cracked in service or develop a slow leak, leading to rejection out of service.

If the bead of the bead mount is melted and softened enough to fuse with the bulb, the above-mentioned troubles are not eliminated. Even then, when the bulb is heated externally, the bulb, having a thinner wall, will be softened sooner than the head of the bead mount; and with the inside of the bulb evacuated, the fused portion of the bulb will suffer greater deformation. This greater deformation will make the areas other than the fused position between the. bulb and the bead of the bead mount liable to develop a crack due to excessive melting of the bulb.

Thus, the lamps produced by this method develop a slow leak just like the lamps with imperfect fusion.

If mass production is to be accomplished according to the second method, fusion may be done by placing in a vacuum heating furnace tube a jig which holds a larger number of bulbs and bead mounts. However,

' many troubles occur in this case. In moving the jig up to the heating position in the furnace tube, the relative position of the bead mount of the bulb is disturbed by vibration, etc., resulting in rejects due to imperfect fusion or deformed fusion. Extreme cautionis required in handling the jig which holds bulbs and bead mounts and the manufacturing time in relatively long.

In the case of the third method, rejects due to imperfect fusion or deformed fusion are also inevitable, because it is difficult to alter the position of the bead mount once the exhaust pipe is connected to the'open end of the bulb after the bead mount is set' in position within the bulb; therefore, it is difficult to correct the slightest displacement of the bead mount due to sudden discharge of air through the exhaust pipe.

Thus any of the three conventional methods for manufacturing small electric lamps will result in products of poor quality and short life with many rejects due to manufacturing defects. Accordingly, with high production cost, none of these methods is found to be satisfactory for manufacturing small electric lamps.

BRIEF SUMMARY OF THE INVENTION to prevent rejects in production. The invention prevents infiltration into the bulb of the impure gas generated from the heating element for heating the bead of the bead amount and the bulb and from the jig holding them. According to the present invention there are produced small electric lamps with no infiltration of impure gas in the bulb and perfect fusion of the head of the bead mount of the bulb, thereby preventing development of cracks or slow leaks during service in lamps, preventing deterioration of lamp illumination and prolonging the service life of the lamps.

Further, rejects in production, due to deformed fusion or imperfect fusion are prevented by assuring the accuracy of the relative position of the bead mount to the bulb by allowing the bead mount position within the bulb to be freely and easily changed up to the moment just before the bulb is fused to the bead of the bead mount. I

To fulfill these objectives, in the present invention the open end of the bulb holding the entire filament-attached bead mount is fused and sealed with a vacuum in the bulb by some known method, thereby yielding the primary product.

Next, by gently tapping the bulb. the bead mount is reset to the correct position within the bulb. The bulb is placed at the center of a heating element of evacuation equipment, which internally supports the heating element, which in turn is installed is such manner so as to surround the part of the bulb to be fused. With the interior of the evacuation equipment evacuated, the heating element is heated, thereby fusing together the bulb and the bead of the bead mount.'Finally the unnecessary portion of the fused bulb is cutoff to produce a small electric lamp, i.e., the final product.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the method and apparatus according to the present invention and the small electric lamp produced thereby will be understood by reading the following detailed description with reference to the ,attached drawings. Alteration or modifications in details of this invention are covered by the attached claims.

In the attached drawings, 1

FIG. 1 is a sectional view of the primary product obtained by a known method;

FIG. 2 shows an embodiment of the apparatus for manufacturing small electric lamps according to the present invention;

FIG. 3 is a partial perspective view of the apparatus in FIG. 2;

FIG. 4 shows another embodiment of the apparatus for manufacturing small electriclamps according to the present invention;

FIG. 5 is a plan view of a part of the apparatus in FIG. 4;

FIG. 6 A is a sectional view showing the state of fusion between the bulb andthe bead of the bead mount;

FIG. 6 B is a sectional view of a finished product with I the unnecessary portion of fused bulb cut off; I

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the manufacturing method and the apparatus for producing small electric lamps according to the present invention and small electric lamps thus produced will be described with reference to the corresponding drawings. In these drawings the same symbols indicate the same components.

Referring to FIGS. 1, 2, 3, 6A, and 63, at first the upper side of a pair of lead wires 1, 2, separated by a certain gap, are beaded. Between the top ends of wires 1 2, filament 3 is stretched, thereby constituting a bead mount a. Bead mount a, with the bottom of lead wires 1, 2 opened, isinserted into a soft glass bulb 4 with the top sealed and the bottom opened. Then, utilizing the elasticity of wires 1, 2, bead mount a is fixed in a predetermined position within bulb 4.

Next, using known means, bulb 4 is evacuated to about I X l0'*'mmHg. Then by melting and subsequently scaling up the open end of the bulb, a primary product, as shown in FIG. 1, with both ends of bulb 4 sealed, is obtained. Thereafter, bead mount a in bulb 4, which has been displaced within the bulb during evacuation, is readjusted to the correct position by lightly tapping either the head or the sealed portion of bulb 4. Then, the primary product, with bead mount a thu's reset, is inserted, with its head down, into receiving hole 6 of bulb stand 5, fabricated of insulating material. Bulb 4 is inserted in evacuation equipment b in such a way that the part of the bulb to be fused and sealed projects out of the hole. Above bulb stand 5, at the level of the fusion between bead 7 of bead mount a and bulb 4, a high frequency heating carbon ring 8 is supported on three legs 9. A metal plate 10 extends from the side of stand 5 to the top of high frequency heating ring 8 and it terminates as a bulb-clamp 10' for holding the top portion of bulb 4 in an upright position. Around high frequency heating ring 8 is rigidly fitted to high frequency heating coil 12 connected to high frequency generator 11 provided outside of evacuation equipment b, said high frequency heating coil 11 surrounding high frequency heating ring 8. At the center of evacuation equipment b, is a charge-discharge pipe 15 which is equipped with a vacuum cock 13 and an air release cock 14. After the primary product is thus positioned atthe top of evacuation equipment b, the top is closed covering all the elements provided or set on the top thereof, i.e., stand 5, high frequency heating ring 8, high frequency heating coil 12 and bulb 4, with a hard glass external cover 16 with the bottom opened. The open bottom part is airtightly inserted into external cover insertion slot 17 provided in evacuation equipment b. In this statevacuum cock 13 is opened and the space under external cover 16 is evacuated to a vacuum of about 1 X 10* 10*mmI-Ig. Thereafter high frequency heating ring 8 is heated by means of high frequency generator 11 and its heating coil 12, thereby fusing together bead 7 of bead mount a and bulb 4.

After fusion is completed, the power supply to high frequency heating coil 12 is cut off and after several minutes, the fused portion of the bulb becomes smooth as a result of residual heat. Thereafter vacuum cock 13 in evacuation equipment b is shut and air release cock 14 is opened to bring the space under external cover 16 to atmospheric pressure. Then, external cover 16 is removed from the evacuation equipment and the fused bulb is taken out of hole 6 in stand 5 by unfitting bulbclamp 10'. From removed bulb 4, the unnecessary portion below the fused area, as shown in FIG. 6 A, is cut off by a cutter 24 or the like, providing the final product, i.e., a small electric bulb C as shown in FIG. 6 B. In this Figure, an airtight rubber ring 18 is used to provide an airtight seal for external cover 16 fitted in external cover insertion slot 17; stand prop 19 suspends stand 5 above evacuation equipment b. Meanwhile, airtight rubber packings 20, 21 preventleakage from the space between lead wires 22, 23 of high frequency generator 11 and evacuation equipment b.

Referring now to FIGS. 1, 4, 5, 6A and 6B, the same method and equipment as the previous embodiment are used to manufacture small electric lamps, the principal difference being that the heating element for fusing together bulb 4 and bead 7 of bead mount a is not a high frequency type but a resistance type. In the evacuation equipment b of this embodiment, the top end of charge-discharge pipe 15, equipped with vacuum cock 13 and air release cock 14, is attached on the underside at the center of evacuation equipment b to open at the top side of evacuation equipment b. On the top side at the center of the evacuation equipment, a stand 5' with three holes 6' bored at equal intervals to receive the head of bulb 4, and a bulb-fixture 26 equipped with three bulb-clamps 25 to hold removably bulb 4 above holes 6 of stand 5' by means of the fitting rods 27, 28. Above stand 5', at the same level as the part of bulb 4 to be fused, resistance heating element 29 is fitted by means of conductive rods 30, 30, 31, 31' in such a manner as to surround bulb 4. Conductive rods 30, 30', 31, 31' are alternately connected to lead rods 32, 33 for connection to the power source positioned outside of evacuation equipment b. In the figures, lead wires 34, 35 link the conductive rods 30, 31 to the lead rods 32, 33 and cords 36, 37 connect lead rods 32, 33 to the power source. A stainless filter 38 is attached to the top end of charge-discharge pipe to prevent glass pieces or dust from getting into charge-discharge pipe 15. Otherwise the arrangement is the same as in the previous embodiment. Therefore, when bulb 4 and bead 7 of the bead mount a are to.be fused together using the equipment of this embodiment, the primary product obtained in the same way as previously described is set in a predetermined position for bead mount within the bulb. Then bulb 4, with its head directed downwardly, is inserted through bulbclamp 25 of bulb-fixture 26, into hole 6 of stand 5' in evacuationequipment b. Next the whole assembly is placed under an external cover 16, whose bottom is rigidly fitted into external cover insertion slot 17. After covering is completed, vacuum cock 13 is opened and the space under external cover 16 is evacuated to a vacuum of about 1 X 10' l0"mmHg. Then current is passed from the power source to resistance heating element 29 to heat element 29, thereby fusing together bulb 4 and bead 7 of bead mount a.

After fusion, current to resistance heating element 29 is cut off and in the same way as previously described, the fused portion is made smooth. When fused bulb 4 is taken out of evacuation equipment b, by cutting off the unnecessary portion as indicated in FIG. 6 A by cutter 24, the final product, as shown in FIG. 6 B, i.e., a small electric lamp C is obtained.

In the foregoing embodiments, the degree of vacuum within the bulb or under the external cover, temperature of the heating element and the duration of heating depend on the size and wall thickness of the small electric lamps to be manufactured or on the bead size of the bead mount; and these factors may be adequately predetermined according to known technical means.

Although there is no exact numerical limitation on the degree of vacuum outside of and inside of the bulb, the degree of vacuum should be greater on the inside than on the outside so that the difference in pressure and surface tension promotes contact between the bead and bulb during fusion.

The embodiments of the invention as described are not restrictive; therefore, an increase in dimension of the equipment for purposes of fusing a large number of bulbs at the same time on an efficient mass production basis, and other alternations of the equipment are contemplated by the attached claims.

For purposes of comparison, the manufacture of small electric lamps in accordance with conventional methods is to be described hereinafter with reference to the corresponding drawings.

Method 1 (Figure 7) FIG. 7 illustrates the state immediately before evacuation. In the Figure, an airtight box 41 is equipped with an exhaust pipe 42 leading to the exhausting equipment and an air release pipe 43 to communicate with the atmosphere. These pipes are each provided with a vacuum cock 44 and an air release cock 45. Lid 46 is dismountably fitted to airtight box 41; this lid is constructed rugged enough to withstand the conditions when air-tight box 41 is sealed and evacuated. Mount-support rod 47 is slidably inserted at the center of the lid 46 without breaking the airtightness of lid 46. This rod has a mount grip 48 at its bottom and it is elastically held to the lid by means of a stopper 49 fixed at its top and a spring 50 movably fitted beneath this stopper. A heating element 51 is installed within airtight box 41. This element consists of a nichrome wire or the like formed in a coil; it is located surrounding fringe 52' of bulb 52 installed in a predetermined position in airtight box 41 and it is connected to an external power source. Element 53 is a ring-shaped support, and 54 is a support stand. Both are placed within airtight box 41 to support bulb 52 therein at a predetermined position. Bead mount a comprises a pair of lead wires 56, 57 fitted to its bead 55 and a filament 58 attached to the tips of these wires. The bead mount is inserted into bulb 52 with the ends of the lead wires held by mount grip 48, in such manner that bead 55 may be positioned nearly at the same level I as fringe 52' of the bulb.

Next, to describe the manufacture of small electric lamps using this'equipment, at first vacuum cock 44 is opened to fully exhaust the air out of airtight box 44; then cock 44 is shut. Thereafter, current is passed to heating element 51; heating element 51,,when hot, heats bulb fringe 52' to a temperature high enough to soften and melt. Thereby fringe 52 contracts inwardly to narrow the mouth ,of bulb 52 until it approaches to lead wires 56, 56. At the same time, bead 55 also softens and melts to seal up the lead wires, whereupon the current supply to heating element 51 is cut off, and mount support rod 47 is depressed to join bead 55 to bulb fringe 52, thereby fusing them together to seal up bulb 52 airtight. Thus, the final product, a small electric lamp, is obtained.

Method 2 (FIG. 8, 9)

To manufacture a small electric lamp by this method, at first a bead mount a with a head 60 wide enough to be able to engage the open edge of bulb 59 is inserted, with the filament down, into inverted bulb 59. Then this bulb is inserted, with bead 60 and the fringe of bulb 59 exposed, into a hole bored on the top of a jig 61 fabricated of a material, such as carbon or metal, which does not fuse to glass and is heat-resistant. In this state jig 61 is placed in a heating furnace. The heating furnace contains a tube 62 made of heat-resistant material like quartz or metal; heating resistant wire 64 is wound around the outside of heating part 63 near the midpoint of tube 62, the heating part 63 is wrapped with a heatshielding material 65, such as magnesia, and further outside a surrounding wall 6 is provided. Lead terminals 67, 68 of heating resistance wire 64 are provided on the surrounding wall. Respectively at inlet 69 and outlet 70 to tube 62 are installed air-insulting doors 71, 72; and midway between these doors 71, 72 and heating part 63 are positioned exhaust pipe 73 to evacuate tube 62 and air release pipe 74 to introduce air into tube 62. lnside of tube 62 a support stand 75 is arranged to carry jig 61; and to this stand 75 is fitted a metal wire 76 by which stand 75 is carried from inlet 69 to outlet 70.

.lig 61 is carried on stand 75. By manipulation of metal wire 76, jig 61 is positioned at heating part 63 within the tube 62, and air is exhausted to create a vacuum by closing inlet 69 and outlet 70 and opening cock 73 of exhaust pipe 73 in tube 62.

Then, current is passed to made the heating element hot, whereupon radiant heat from the inside wall of tube 62 melts and softens the exposed bead 60 and the fringe of bulb 59 on the top of jig 61, thereby effecting the seal. After fusion and sealing, cock 73' of exhaust pipe 73 is closed and cock 74' of air release pipe 74 is opened to introduce air into tube 62; and by manipulation of metal wire 76 with the doors 7], 72 being open, jig 61 is carried out of tube 62, providing the finished product, a small electric lamp.

Method 3 (FIG. 10)

To manufacture a small electric lamp by this method, at first the entire bead mount a, with lead wires 1, 2 outstretched, is inserted into bulb 4 and, utilizing the elasticity of lead wires 1, 2, head mount a is fixed in position within bulb 4.

Next, the open end of bulb 4 is airtightly connected to exhaust pipe 77 communicating with the exhausting equipment; bulb 4 is exhausted to vacuum; thereafter from both sides of head mount a at the outside of bulb 4, gas burners 78, 79 are applied to melt and soften the part of bulb 4 to be fused and head 5 of the bead mount a, thereby fusing them together. After fusion, exhaustion by exhaust pipe 77 and heating by gas burners 78,79 are halted; bulb 4 is disconnected from exhaust pipe 77; and the unnecessary portion of the bulb is cut off to produce finally a small electric lamp.

As fully explained above, the conventional methods (l-3) for manufacturing small electric bulbs have a number of drawbacks, which, however, can be completely eliminated by the manufacturing method and equipment as proposed by this invention. Because according to the present invention the entire filamentattached bead mount is vacuum-sealed within a bulb by a known method to yield a primary product and this bulb is fused with the bead of the bead mount, there is no possibility of impure gas generated from the heating element, etc. being enclosed within the bulb during fusion. Moreover, there is no convection of heat taking place under the external cover at the time of fusion between the bulb and the bead of the bead mount and, accordingly, the part to be fused can be locally exposed to sufficient heat. Thus, perfect and reliable fusion between the bulb and the bead of the bead mount are assured by controlling the degree of vacuum under the external cover and the bulb heating time during manufacture in accordance with such conditions as the size and wall thickness of the bulb, thereby precluding the possibility of deformed fusion, insufficient fusion or fusion strain in the bulb. Further, since the bead mount position of a bulb can be freely adjusted up to the moment just before the fusion is done, variance along the whole length of the product can be prevented and accordingly uniform production with no rejects is assured.

As in the embodiment of FIG. I, when a high frequency heater is adopted as the power source for fusion of the head of the bead mount to the bulb, the heat from the high frequency heating ring and the self-induction heat from the bulb and the bead-glass in a semi-molten state develops a self-induction heat, which promotes heating and melting of the part to be fused and produces a more perfect, reliable and smooth fusion.

Small electric lamps produced by the method and equipment of the present invention have perfectly fused bulbs which contain no impure gas; therefore they are not likely to develop cracks or slow leaks under varied temperature and vibration in service.

Thus, the method of the invention can simplify mass production of high quality small electric lamps'with no deterioration of illumination and with maximum service life. Moreover, since the equipment is simplified and its operation is easy, the'manufacture requires no skilled labor. Thus, even a non-skilled worker can produce the lamps without any loss because of rejects. Besides, the equipment can be readily automated for mass production with increased efficiency. Meanwhile,

annealing, to correct the deformation of the joint after the fusion of bead and bulb is completed, is obviated and in consequence the finished product can be low in cost.

As seen'from the above description, the method of manufacturing small electric lamps according to this invention, small electric lamps thus produced and the manufacturing equipment to be used have a number of industrial advantages over the conventional methods of manufacturing small electric lamps, small electric lamps thus produced and the manufacturing equipment to be used therewith.

What is claimed is:

1. A method for manufacturing small electric lamps comprising a. inserting a filament-attached bead mount into a bulb;

b. evacuating said bulb;

c. fusing and sealing said evacuated bulb with the entire bead mount contained therein;

d. adjusting the bead mount to a proper predetermined position within the bulb;

e. placing the bulb in an evacuation zone and evacuating said zone;

f. heating the bulb in the area adjacent the bead mount to cause melting of the bulb wall and fusion of the bulb to the bead of the bead mount;

g. gradually cooling the fused portion of the bulb to create a smooth seal at the point of fusion; removing the fused bulb from the evacuation zone;

and i. cutting off the unnecessary portion of the bulb below the point of fusion to provide a small electric lamp.

2. The method of claim 1 wherein the degree of adjust the bead mount to a proper position. vacuum within the bulb is 1 X 10- to IO' mmI-ig and 4. The method of claim 1 wherein the bulb is heated the degree of vacuum in the evacuation zone is l X 10' by a high frequency carbon heating element. to 10 5. The method of claim 1 wherein the bulb is heated 3. The method of claim 1 wherein the sealed evacu- 5 y a resistance heating elementated bulb containing the entire bead mount is tapped to 

1. A method for manufacturing small electric lamps comprising a. inserting a filament-attached bead mount into a bulb; b. evacuating said bulb; c. fusing and sealing said evacuated bulb with the entire bead mount contained therein; d. adjusting the bead mount to a proper predetermined position within the bulb; e. placing the bulb in an evacuation zone and evacuating said zone; f. heating the bulb in the area adjacent the bead mount to cause melting of the bulb wall and fusion of the bulb to the bead of the bead mount; g. gradually cooling the fused portion of the bulb to create a smooth seal at the point of fusion; h. removing the fused bulb from the evacuation zone; and i. cutting off the unnecessary portion of the bulb below the point of fusion to provide a small electric lamp.
 2. The method of claim 1 wherein the degree of vacuum within the bulb is 1 X 10 6 to 10 8mmHg and the degree of vacuum in the evacuation zone is 1 X 10 2 to 10
 4. 3. The method of claim 1 wherein the sealed evacuated bulb containing the entire bead mount is tapped to adjust the bead mount to a proper position.
 4. The method of claim 1 wherein the bulb is heated by a high frequency carbon heating element.
 5. The method of claim 1 wherein the bulb is heated by a resistance heating element. 